Are the cramps alleviated by passing gas or having a bowel movement? Or do they occur on their own? Just curious.
When my IBS is acting up, I will get spasms and pains in my lower abdominal region without experiencing a bowel movement or passing gas. It often feels like someone is wringing out my guts or squishing them up like an accordian. I have been tested for everything under the sun, and the conclusion is it is all related to my IBS-D. Hormore fluctuations often cause my IBS to flare. Not sure about menopause because I'm not there, but I bet your hormones are out of whack and that could very well cause some IBS pain.
However, if the pain continues and you're concerned it never hurts to go back to your doc (maybe your GI or Internal Practitioner rather than your OB-GYN) and ask for more testing to rule out other causes.